W77E058A Datasheet, PDF (9/87 Pages) Winbond – 8-BIT MICROCONTROLLER

W77E058A
6. MEMORY ORGANIZATION
The W77E058 separates the memory into two separate sections, the Program Memory and the Data
Memory. The Program Memory is used to store the instruction op-codes, while the Data Memory is
used to store data or for memory mapped devices.
6.1 Program Memory
The Program Memory on the W77E058 can be up to 64 Kbytes long. There is also on-chip ROM
which can be used similarly to that of the 8052, except that the ROM size is 32 Kbytes. All instructions
are fetched for execution from this memory area. The MOVC instruction can also access this memory
region. Exceeding the maximum address of on-chip ROM will access the external memory.
6.2 Data Memory
The W77E058 can access up to 64Kbytes of external Data Memory. This memory region is accessed
by the MOVX instructions. Unlike the 8051 derivatives, the W77E058 contains on-chip 1K bytes
MOVX SRAM of Data Memory, which can only be accessed by MOVX instructions. These 1K bytes of
SRAM are between address 0000H and 03FFH. Access to the on-chip MOVX SRAM is optional under
software control. When enabled by software, any MOVX instruction that uses this area will go to the
on-chip RAM. MOVX addresses greater than 03FFH automatically go to external memory through
Port 0 and 2. When disabled, the 1KB memory area is transparent to the system memory map. Any
MOVX directed to the space between 0000H and FFFFH goes to the expanded bus on Port 0 and 2.
This is the default condition. In addition, the W77E058 has the standard 256 bytes of on-chip
Scratchpad RAM. This can be accessed either by direct addressing or by indirect addressing. There
are also some Special Function Registers (SFRs), which can only be accessed by direct addressing.
Since the Scratchpad RAM is only 256 bytes, it can be used only when data contents are small. In the
event that larger data contents are present, two selections can be used. One is on-chip MOVX
SRAM , the other is the external Data Memory. The on-chip MOVX SRAM can only be accessed by a
MOVX instruction, the same as that for external Data Memory. However, the on-chip RAM has the
fastest access times.
FFh
80h
7Fh
00h
Indirect
Addressing
RAM
Direct &
Indirect
Addressing
RAM
SFRs
Direct
Addressing
FFFFh
64 K
Bytes
External
Data
Memory
03FFh
0000h
1K Bytes
On-chip SRAM
0000h
FFFFh
External
Program
Memory
7FFFh
0000h
32K Bytes
On-chip
Program
Memory
Figure 1. Memory Map
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Publication Release Date: April 17, 2007
Revision A10